Method for regenerating an exhaust gas filtering device for diesel engine and device therefor

ABSTRACT

The invention concerns a method for regenerating a device filtering exhaust gases produced by a diesel engine, said method being of the type wherein particles, retained on a filtering means ( 22 ) of the filtering device, are burnt by the action of a combustion catalyst system. Said method consists essentially in retaining the hot exhaust gases around the filtering means ( 22 ) so as to feed to the particles, at least part of the heat energy required for their combustion and in burning said particles to regenerate the filtering device. The invention also concerns a device for implementing the method, comprising a means for producing a combustion catalyst ( 20 ), a filtering means ( 22 ) of exhaust gases and a diesel oil injecting means, the means for producing a combustion catalyst and filtering means being contained in a reaction chamber ( 18 ).

The present invention relates in general to the field of particle filters and, more particularly, to a method for regeneration of an exhaust gas filtration device for a diesel engine.

Furthermore, the present invention also relates to a filtration device intended to retain the carbon-based and soot particles produced by the engine, and to burn them regularly in order to prevent them from accumulating, the latter phase constituting the regeneration to which the method according to the invention relates.

The development of the industrial age has led to serious consequences for the environment. Specifically, pollution-generating industries as well as automobiles are the source of a significant discharge of pollutants into the atmosphere, which is leading to its modification. This modification is twofold. Firstly, a chemical modification is observed. This is reflected especially by a continuing increase in the air concentration of compounds derived from carbon. These compounds are, in particular, carbon monoxide (CO) and certain unburnt hydrocarbons due to incomplete combustion. The presence of these compounds in the atmosphere constitutes a much more significant direct health risk. For instance, CO is a very powerful respiratory toxin. Polycyclic aromatic hydrocarbons (PAHs) such as benzopyrene, benzanthracene as well as fluoranthrene, which are particularly common in smoke, dust or engine exhaust gases, are known carcinogens.

The atmosphere is also being modified by the release of solid particles. These particles are classified according to their size. The smallest particles, referred to as unsedimentable particles because they cannot be deposited on the ground under the effect of gravity, are the most dangerous for human health because they are capable of entering the pulmonary alveoli. They furthermore contaminate the uppermost layers of the atmosphere and are therefore responsible for global pollution.

In view of this alarming fact, the public authorities at both the national and international level are therefore attempting to establish pollution control standards. These standards pertain to the automobile industry in particular. Automobile companies therefore regularly have to make modifications to their vehicles in order to bring them into compliance with these standards.

Besides the development of new engines having a lower and lower fuel consumption, more particular efforts have been made to develop new exhaust systems intended to reduce the emission of unburnt polluting gases and solid particles. Automobile manufacturers have therefore developed catalytic converters or catalyzers, generally consisting of a stainless steel casing, a thermal insulator and a honeycomb support impregnated with precious metals such as platinum or rhodium. These catalyzers make it possible to reduce the emissions of polycyclic hydrocarbons and CO, in particular, and to do so in a proportion of the order of 50%. However, they have no effect on solid particle emissions. These catalyzers do not therefore offer any significant improvement in the air quality, particularly as regards diesel engines which produce a great deal of solid particles.

Other techniques have been developed in order to limit the emission of polluting particles by vehicles. One of these is the particle filter. This filter makes it possible to reduce by 90% the total mass of particles emitted by diesel engines. It is even more effective for the retention of very fine particles, for which the retention factor can be as much as 99%.

The particle filter, however, requires regeneration in order to burn the particles that have been trapped. The particles are generally trapped by a filtering cartridge which is a component of the particle filter. In order to withstand the elevated temperatures involved, this cartridge may consist of a porous body of cordierite, quartz or silicon carbide, generally with a honeycomb structure so as to provide a maximum surface area for filtration.

One major drawback of such a particle filter consists in the incomplete combustion of the particles retained by the filtering cartridge. This is because, under the conditions of urban use, the temperature reached by the exhaust gases is insufficient to cause their combustion, significantly reduce the clogging of the filter and therefore regenerate it. Without chemical assistance, the carbon-based particles produced by the combustion of diesel fuel in diesel engines will not begin to oxidize significantly until above 500° C. These temperatures are almost never reached under urban driving conditions.

It therefore seems necessary to employ a chemical method in order to eliminate these particles. Various techniques are used in order to permit their combustion.

A first technique consists in providing, upstream of the filter, a catalyst for the oxidation of the nitrogen monoxide (NO) contained in the exhaust gases into nitrogen dioxide (NO₂), the latter having the property of catalyzing the combustion of the carbon-based particles beginning at 250° C. This method, however, necessitates the use of a diesel fuel in which the sulfur content is less than 50 ppm (parts per million), in order to maintain sufficient NO to NO₂ conversion efficiency.

This technique, which is referred to as “Continuous Regenerating Trap” (C.R.T.), combines the effects of the particle filter and of the NO oxidation catalyst. In order to ensure satisfactory operation of the filters, this system requires regular regeneration which reduces the pressure drop across the filter while eliminating the risk of uncontrolled and exothermic regeneration.

Such operation is obtained only when the exhaust gases or the combustion enclosure are at a temperature in excess of 300° C. for at least 30% of the operating time of the vehicle.

Otherwise, violent reactions connected with the excessive concentration of carbon-based particles clogging the filter are developed. These reactions consist in the unduly rapid combustion of a large mass of particles, which generally leads to destruction of the filter by thermal shock, since the temperatures reached are locally very high.

Other techniques resort to the use of organometallic additives put into the diesel fuel, such as cerium, iron, strontium, calcium or the like. These techniques make it possible to obtain an effect similar to that obtained with NO₂, by catalyzing the combustion of the carbon-based materials at temperatures of around 300° C.

A first drawback of these techniques is the prohibitive cost of the additives which are used.

Another major drawback resides in the fact that it is necessary to provide an extra additive delivery device.

Yet another drawback of these techniques is that they have an even greater susceptibility to clogging of the filter, and therefore to the reactions which result from this, if the temperatures reached during operation are not high enough, since the additives present in the carbon-based materials contribute even more to rapid blocking of the filtering medium.

Other techniques have consisted in experimenting with devices based on extra heating means such as burners, electrical resistors or the like. These extra heating means are employed only when the cartridge is beginning to clog up, which entails an increase in the pressure drop. Such a regeneration device is employed with the engine running, that is to say when there is a significant flow rate of exhaust gas. Such a device therefore requires a large heating power in order to heat the exhaust gases and the mass of the filtering cartridge simultaneously to the appropriate temperature.

In such a technical context, it is an object of the present invention to provide a method for regeneration of a filtration device which overcomes the drawbacks of the existing technical difficulties, consisting in dealing with the carbon-based and soot particles emitted by diesel engines.

It is another object of the invention to provide a regeneration method which thus avoids any risk of particle accumulation in the filtration device, and therefore any risk of uncontrolled regeneration.

It is yet another object of the invention to provide a regeneration device which does not lead to significant additional fuel consumption and, more generally, does not lead to additional financial cost for the user.

It is yet another object of the invention to provide a regeneration device which does not degrade the performance of the engine, in particular through pressure drops due to the backpressure exerted by the exhaust gases on the engine when the filtration device becomes clogged.

Lastly, it is a final object of the invention to provide a filtration device for carrying out the regeneration method according to the invention.

These objects, among others, are achieved by the present invention which relates firstly to a method for regeneration of a device for filtering the exhaust gases produced by a diesel engine, this method being of the type in which particles retained on a filtration means of said filtration device are burnt through the action of a combustion catalyst. This method consists essentially in retaining the hot exhaust gases around the filtration means in order to provide the particles with at least some of the heat energy necessary for their combustion, and in burning said particles so as to regenerate the filtration device.

According to one variant, this method also consists in:

-   -   employing a combustion catalyst production means in the         filtration device,     -   measuring a temperature θ_(m) in the vicinity of the combustion         catalyst production means,     -   comparing θ_(m) with a temperature θ_(r) corresponding to the         temperature at which the combustion of diesel fuel in the         presence of the combustion catalyst is complete,     -   if θ_(m) is greater than or equal to θ_(r), initiating         post-injection of diesel fuel through an injection means into         the filtration device for a determined period of time, so as to         cause a temperature rise of the particles in order to permit         their combustion.

According to yet another variant, this method also consists in:

-   -   measuring a pressure P_(m) in the vicinity of the combustion         catalyst production means, said pressure P_(m) reflecting the         degree of obstruction of the filtration means by the particles,     -   measuring the temperature θ_(m),     -   comparing said pressure P_(m) with a reference pressure P_(r)         corresponding to the maximum acceptable degree of obstruction,     -   comparing θ_(m) with θ_(r) if P_(m) is greater than or equal to         the pressure P_(r),     -   initiating the post-injection of diesel fuel if θ_(m) is greater         than or equal to θ_(r).

The invention also relates to a filtration device for carrying out the regeneration method according to the invention. This device has a combustion catalyst production means, a means for filtration of said exhaust gases downstream of said combustion catalyst production means, and a means for injecting diesel fuel upstream of said combustion catalyst production means, said combustion catalyst production means and filtration means being contained in a reaction enclosure along the flow path of the exhaust gases produced by an engine.

The filtration means, consisting of a set of filtering units, is exposed in a chamber for receiving the exhaust gases, with said exhaust gases heating the filtering units.

The filtration means preferably consists of at least two particle filters having a body, formed by the filtering units which are connected together by a joint, and a metal casing.

The means for injecting diesel fuel advantageously communicates with a line for discharging the exhaust gases.

According to another preferred feature, this injection means comprises a diesel fuel reservoir and a chamber for injecting the diesel fuel contained in said reservoir into the discharge line.

The chamber injection chamber is thus supplied, on the one hand, with diesel fuel through a first line connecting it to said reservoir and, on the other hand, with compressed air through a second line connecting it to the engine, said chamber having an orifice through which the diesel fuel is injected into the filtration device.

The device advantageously has an electronic control module.

The device also includes at least one temperature sensor, placed inside said enclosure, used to measure the temperature θ_(m) in its interior.

According to another noteworthy variant, it also includes at least one pressure sensor, placed inside said enclosure, used to measure the pressure P_(m) in its interior.

It is noteworthy that the electronic control module is connected to the temperature and pressure sensors, compares the respectively measured values of θ_(m) and optionally P_(m) with the reference values θ_(r) and optionally P_(r), and initiates the injection of diesel fuel into the discharge line through said injection system when the measurements θ_(m) and optionally P_(m) are greater than or equal to the reference values θ_(r) and optionally P_(r).

The lines supplying the chamber of the injection system with diesel fuel and compressed air each advantageously have a solenoid valve controlled by the electronic control module, opening of the solenoid valves leading to the intake of diesel fuel and compressed air into the chamber, and therefore to the injection of diesel fuel into the exhaust gas discharge line.

The chamber of the injection system is advantageously provided with a nozzle in front of the orifice, making it possible to inject the diesel fuel in a nebulized form into the gas discharge line.

The filtering units are advantageously made of silicon carbide or any other equivalent material whose structure is of a honeycomb type.

According to another noteworthy feature of the invention, the combustion catalyst production means consists of at least one cartridge based on platinum or any equivalent material that catalyzes the conversion of the nitrogen monoxide (NO) contained in the exhaust gases into nitrogen dioxide (NO₂).

According to another noteworthy feature, the capacity of the second reservoir is preferably equivalent to the maximum volume of diesel fuel injected during the post-injection.

The particle filters are advantageously placed in parallel in the filtration device.

The present invention will be understood more clearly on reading the following description, given with reference to the drawings which represent an exemplary embodiment of the filtration device according to the invention without implying any limitation, and in which:

FIG. 1 represents a schematic overall view of the system which comprises the filtration device and makes it possible to carry out the regeneration method.

FIG. 2 represents a view in longitudinal section of the filtration device according to a first embodiment.

FIG. 3 represents a view in cross section, on the axis II-II, of the filtration device represented in longitudinal section in FIG. 3.

FIG. 4 represents a variant of the latter embodiment, seen in a longitudinal section of the filtration device.

FIG. 5 represents a view in longitudinal section of the filtration device according to a second embodiment.

The system for carrying out the regeneration method according to the invention is schematically represented in FIG. 1, according to a preferred embodiment. Various mechanical elements of the vehicle, which may or may not be components of the filtration device and which contribute to the regeneration of the device, cooperate in this system.

A diesel engine 10, supplied with fuel from a main reservoir 12 via a supply system 14, produces exhaust gases during operation. These gases are recovered using a manifold (not shown) at the outlet of the engine, and are discharged through a discharge line 16. This line enters an enclosure 18 containing a combustion catalyst production means 20 and a filtration means 22. A temperature sensor 24 and a pressure sensor 26 are also placed in the enclosure 18. The function of these sensors is to measure the temperature and the pressure in the vicinity of the combustion catalyst production means. The data relating to these measurements are transmitted to an electronic control module 28, by which they are analyzed.

The electronic control module is connected to two lines 30 and 32 and controls their opening. The line 30 connects a secondary reservoir 34 to the injection chamber 36. The secondary reservoir 34 supplies the injection chamber 36 with diesel fuel. It is itself supplied from the main reservoir 12 through a pipe system 38.

For its part, the line 32 connects the engine 10 to the injection chamber 36. It allows the engine 10 to supply the injection chamber 36 with compressed air.

The lines 30 and 32 are opened using two solenoid valves 31 and 33, which are electrically controlled by the electronic control module.

A detailed view of the enclosure 18 in longitudinal section is represented in FIG. 2.

The enclosure contains the combustion catalyst production means 20 and the filtration means 22. The combustion catalyst production means 20 consists of two cartridges 20 a and 20 b for producing combustion catalysts.

These cartridges are preferably on a metal support so as to obtain the least possible thermal inertia. According to a preferred embodiment, these cartridges are preferably based on platinum and the nitrogen monoxide (NO) contained in the exhaust gases is converted inside them into nitrogen dioxide (NO₂), which constitutes the combustion catalyst. The NO₂ which is produced diffuses to the filtration means 22.

The filtration means 22 consists of a set of three-dimensional filtering units. These filtering units are advantageously of the silicon carbide honeycomb type.

According to a first embodiment, which is represented in FIG. 2, these filtering units are assembled so as to form the body of a particle filter. The filtration means accordingly consists of three particle filters 22 a, 22 b and 22 c. These particle filters, arranged in this way, are represented as seen from above in FIG. 3. The filters consist of a body 40 and a metal casing 42. The body 40 is formed by assembling a plurality of filtering units 44 which are separated by a joint 46, the function of which is to compensate for their expansion.

In its lower part, the enclosure 18 contains a retention chamber making it possible to increase the residence time in the enclosure for the exhaust gases purified by passing through the filtration means (filtering units or particle filters).

This extension of the residence time of the exhaust gases allows them to heat the filtering units or the particle filters, and therefore the particles themselves. This noteworthy feature allows the latter to be maintained at a temperature much higher than the usual temperature. This temperature may reach the temperature for their combustion in the presence of the combustion catalyst. In this case, the regeneration takes place without diesel fuel being injected.

A variant of this embodiment is represented in FIG. 4. According to this variant, the particle filters 22 a, 22 b and 22 c are arranged the other way round. The device then has a particular region for retention of the as yet unfiltered exhaust gases. Specifically, the latter are contained between the catalyst cartridges and the lower support 48 of the filters, which allows the exhaust gases to have a longer dwell time before they enter the particle filters, a fact which will, on the one hand, promote the heat exchange between the gases and the filters and, on the other hand, limit the loss of heat by exchange with the surroundings.

According to a second embodiment of the device according to the invention, the filtering units 44 are independent of one another. Accordingly, each filtering unit is separated from the ones adjacent to it by a space sufficient to allow their expansion. This arrangement is particularly advantageous because, on the one hand, it makes it possible to reduce the thermal expansion stresses very significantly, particularly in the event of vigorous combustion of the particles which are retained, which greatly limits the risk that the filtering units will be damaged; on the other hand, the surface area available for the transmission of heat by the gases is increased considerably, which commensurately reinforces this transmission of heat.

A variant of the second embodiment, which is represented in FIG. 5, consists in arranging the filtering units 44 the other way round in the filtration device, with a support being positioned in the lower part, similarly as in the variant of the first embodiment which is represented in FIG. 4. The advantages of this arrangement are the same as those mentioned above in the description of FIG. 4.

According to an exemplary embodiment, each filtering unit is a square-based cylinder having a width and a depth of 35 mm, and a length varying from 150 to 300 mm.

If the temperature is not sufficient to initiate combustion of the particles, the regeneration is carried out by injecting diesel fuel.

In order to do this, the temperature in the vicinity of the catalyst production means is measured using the sensor 24. The measured temperature value θ_(m) is received by the electronic control module. The module compares this value θ_(m) with a reference value θ_(r), corresponding to the temperature at which combustion of the diesel fuel takes place completely in the presence of the catalyst.

If the measured temperature θ_(m) is greater than or equal to the reference value θ_(r), the electronic control module initiates opening of the solenoid valves 31 and 33. This opening leads to the intake of diesel fuel and compressed air into the chamber 36. The diesel fuel mixes with the compressed air in the chamber 36, and the mixture formed in this way is injected in a nebulized form into the gas discharge line 16. This injection is carried out through an orifice arranged in the wall of the chamber 36, in front of which there is a nozzle fixed to the chamber, making it possible to obtain a nebulized jet under pressure. According to an exemplary embodiment, the chamber 36 is of the compressed-air paint spraygun type.

When the necessary quantity of diesel fuel, predetermined by the electronic control module, has been injected, the diesel fuel supply is interrupted by closing the solenoid valve 33. Only the supply of compressed air continues, so that the latter instead of the mixture is injected into the line 16. The purpose of this extended supply of compressed air is to eliminate all the remaining diesel fuel in the injection chamber 36 and the line 16.

The capacity of the secondary reservoir 34 is determined so that it corresponds to the maximum volume of diesel fuel necessary for the regeneration. In this way, excessive consumption of diesel fuel cannot take place. By virtue of this embodiment, the frequency of the regeneration cycles is furthermore limited by the time taken to fill the second very reservoir 34, which also makes it possible to avoid consequent extra fuel consumption.

The fuel injected into the discharge line 16 enters the enclosure and undergoes complete combustion in the catalyst production means. This combustion leads to a significant rise in temperature, up to a temperature θ_(c) at which combustion of the particles clogging the filtration means will take place. The NO₂ molecules which are produced will catalyze this combustion reaction. This reaction therefore takes place at a temperature lower than the normal temperature. During this combustion, the solid particles are converted into gases, which are discharged.

The filtration means is therefore freed from deposits and recovers its full filtration capacity.

According to a particular embodiment, the measurement of θ_(m) may be processed by the electronic module in order to evaluate the temperature of the particles in the filtration means. Specifically, if θ_(m) is close to the temperature at which the particle combustion can take place without post-injection of diesel fuel, the computer may decide not to initiate this post-injection, which allows a substantial fuel saving to be made.

According to a variant of this embodiment, an additional temperature sensor is arranged in proximity to the filtration means, so as to obtain the exact temperature of the particles.

A third mode of operation consists in simultaneously measuring the temperature and the pressure in the catalyst production means, using the temperature sensor 24 and the pressure sensor 26. The measured pressure value P_(m) reflects the degree of obstruction of the filtration means by the particles. Specifically, if the filtration means is clogged, it is more difficult for the exhaust gases to pass through, so that they exert a backpressure. Measuring the pressure P_(m) therefore corresponds to the best way of monitoring the clogging of the filtration means. The electronic control module compares the measured value P_(m) with a reference value P_(r), corresponding to the maximum acceptable degree of obstruction of the filtration means. The electronic control module then initiates the post-injection of diesel fuel if P_(m) is greater than or equal to the pressure P_(r), which leads to regeneration of the filtration means. The benefit of this mode of operation is that the post-injection is initiated only when the filtration means has reached a determined degree of clogging, which allows the extra fuel consumption to be limited greatly.

EXAMPLE

A filtration device used with an industrial vehicle engine is presented below as a nonlimiting example, namely the supercharged Renault VI 620-45 engine with a 10 liter cylinder capacity and a power of 190 kw. This engine is used in city buses.

The filtration device is composed of:

-   -   Two platinum-based catalyst cartridges for converting NO into         NO₂. These cartridges, which are 7.5 inches in diameter and 3         inches long, were fitted in parallel on a metal support as         represented in FIG. 2. The volume of catalyst was determined so         that the NO to NO₂ conversion ratio is more than 85%.     -   Three IBIDEN particle filters, of the silicon carbide honeycomb         type, fitted in parallel. These filters have a cross section of         162 cm² (diameter 143.8 mm) and a length of 254 mm.     -   A diesel fuel injection system having an injection chamber as         described above and a secondary reservoir with a capacity of 50         cm³. The injection system delivery rate is 50 cm³ per minute.         This delivery rate was determined so that the rise in         temperature of the exhaust gases due to the post-injection is         between 170 and 250° C., depending on the conditions of use.     -   An electronic module controlling the post-injection of diesel         fuel. A timer limits the duration of the post-injection to 1         minute, and specific programming of the module makes it possible         to obtain at most one post-injection every 5 minutes.

The trial was carried out on a rig and the conditions corresponding to urban driving conditions.

The electronic module was set so that the post-injection is initiated as soon as the backpressure reaches 120 mb and the temperature of the gases is more than 300° C.

It is known that, in order for the regeneration to take place correctly, it is necessary that the time for which the temperature of the exhaust gases is in excess of 300° C. should be more than 30% of the working time of the vehicle.

The device described in this example makes it possible to obtain an exhaust gas temperature constantly in excess of 300° C., regardless of the initial temperature of the exhaust gases.

The value of the backpressure measured after each regeneration process of the filtration device is thus 50 mb, which corresponds to the backpressure value measured on a new filtration device. The regeneration of the device is therefore complete.

The regeneration method according to the invention, and the associated filtration device, are therefore particularly suitable for processing the exhaust gases of municipal transport vehicles. In fact, the gases produced by these vehicles are generally at a temperature below that necessary in order to allow regeneration of conventional filtration devices, which leads to clogging of these devices and therefore their rapid deterioration owing to vigorous combustion reactions. The results obtained with the present technique, however, make it possible to envisage a minimum lifetime of 100,000 km for the filtration device on vehicles of this type.

Such a technique could also be used in automobiles. In fact, because these operate at much higher engine speeds, the exhaust gases which are produced are at much higher temperatures, possibly in excess of 500° C. The problem of filter regeneration is therefore less crucial. Existing systems, however, generally use organometallic additives in order to catalyze the particle combustion, which leads to a significant operating cost. The device according to the invention, associated with its regeneration method, makes it possible to overcome this problem of cost.

Although the filtration device according to the invention may not include new technical elements, the inventors have succeeded in combining and adapting various existing techniques in order to enhance their effects and obtain a device which has a very high efficiency, in order to combat the emission of polluting particles produced by diesel engines and, furthermore, in order to obtain excellent results in terms of the regeneration of filters, even in the case of vehicles whose engine speeds do not make it possible to obtain exhaust gases which are at high temperature. 

1-19. (Canceled)
 20. A method for regeneration of a device for filtering the exhaust gases produced by a diesel engine in which particles retained on a filtration means of said filtration device are burnt through the action of a combustion catalyst, comprising retaining the hot exhaust gases around the filtration means in order to provide the particles with at least some of the heat energy necessary for their combustion, and burning said particles with at least some of the heat energy necessary for their combustion, so as to regenerate the filtration device.
 21. The method of claim 20, further comprising: employing a combustion catalyst production means in the filtration device, measuring a temperature θ_(m) in the vicinity of the combustion catalyst production means, comparing θ_(m) with a temperature θ_(r) corresponding to the temperature at which the combustion of diesel fuel in the presence of the combustion catalyst is complete, if θ_(m) is greater than or equal to θ_(r), initiating post-injection of diesel fuel through an injection means into the filtration device for a determined period of time, so as to cause a temperature rise of the particles in order to permit their combustion.
 22. The method of claim 21, further comprising: measuring a pressure P_(m) in the vicinity of the combustion catalyst production means, said pressure P_(m) reflecting the degree of obstruction of the filtration means by the particles, measuring the temperature θ_(m), comparing said pressure P_(m) with a reference pressure P_(r) corresponding to the maximum acceptable degree of obstruction, comparing θ_(m) with θ_(r) if P_(m) is greater than or equal to the pressure P_(r), initiating the post-injection of diesel fuel if θ_(m) is greater than or equal to θ_(r).
 23. A device for carrying out the regeneration method of claim 20, comprising a combustion catalyst production means, a means for filtration of said exhaust gases downstream of said combustion catalyst production means, and a means for injection of diesel fuel upstream of said combustion catalyst production means, said combustion catalyst production means and filtration means being contained in a reaction enclosure along the flow path of the exhaust gases produced by an engine.
 24. The device of claim 23, wherein said filtration means, comprising a set of filtering units and is exposed in a chamber for receiving the exhaust gases, with said exhaust gases heating said filtering units.
 25. The devise of claim 24, wherein said filtration means comprises at least two particle filters having a body, formed by the filtering units which are connected together by a joint, and a metal casing.
 26. The device of claim 23, wherein said means for injection of diesel fuel communicates with a line for discharging the exhaust gases.
 27. The device of claim 23, wherein said means for injection comprises a diesel fuel reservoir and a chamber for injecting the diesel fuel contained in said reservoir into the discharge line.
 28. The device of claim 27, wherein said chamber is supplied, on the one hand, with diesel fuel through a first line connecting it to said reservoir and, on the other hand, with compressed air through a second line connecting it to the engine, said chamber having an orifice through which the diesel fuel is injected into said filtration device.
 29. The device of claim 23, further comprising an electroinc control module.
 30. The device of claim 23, further comprising at least one temperature sensor, placed inside said enclosure and adapted to measure the temperature θ_(m) in its interior.
 31. The device of claim 23, further comprising at least one pressure sensor, placed inside said enclosure and adapted to measure the pressure P_(m) in its interior.
 32. The device of claim 30, wherein the electronic control module is connected to a temperature sensor and to a pressure sensor, and compares the respectively measured values of θ_(m) and optionally P_(m) with the reference values θ_(r) and optionally P_(r), and initiates the injection of diesel fuel into the discharge line through said injection system when the measurements θ_(m) and optionally P_(m) are greater than or equal to the reference values θ_(r) and optionally P_(r).
 33. The device of claim 32, wherein the lines supplying the chamber of the injection system with diesel fuel and compressed air each have a solenoid valve controlled by the electronic control module, opening of the solenoid valves leading to the intake of diesel fuel and compressed air into the chamber and therefore to the injection of diesel fuel into the exhaust gas discharge line.
 34. The device of claim 28, wherein the chamber of the injection system is provided with a nozzle in front of the orifice, making it possible to inject the diesel fuel in a nebulized form into the gas discharge line.
 35. The device of claim 24, wherein the filtering units preferably consist of silicon carbide or any other equivalent material whose structure is of a honeycomb type.
 36. The device of claim 23, wherein the combustion catalyst production means comprises at least one cartridge based on platinum or any equivalent material that catalyzes the conversion of the nitrogen monoxide (NO) contained in the exhaust gases into nitrogen dioxide (NO₂), the NO₂ which is produced catalyzing the combustion reaction of the particle clogging the filter.
 37. The device of claim 23, wherein the capacity of the second reservoir is preferably equivalent to the maximum volume of diesel fuel injected during the post-injection.
 38. The device of claim 25, wherein the particle filters are placed in parallel in the enclosure. 